This application relates to a seal for defining a back pressure chamber in a scroll compressor, wherein the seal is non-circular, but still centered on a center axis.
Scroll compressors are becoming widely utilized in refrigerant compression applications. In a scroll compressor, a first scroll member has a base with a generally spiral wrap extending from the base. A second scroll member has its own base and spiral wrap. The two wraps interfit to define compression chambers. One of the two scroll members is caused to orbit relative to the other. As relative orbital movement occurs between the wraps, the size of the compression chambers is reduced, thus compressing an entrapped refrigerant.
While scroll compressors are becoming very successful, they do raise certain design challenges. One challenge is that the compressed refrigerant tends to force the two scroll members away from each other. This so-called “separating force” would cause the wraps to move out of contact with the base of the opposed scroll member, and reduce the efficiency of compression. Hence, a back pressure chamber has been created in known scroll compressors.
The back pressure chamber taps a small amount of compressed refrigerant to an area which resists movement of one of the two scroll members away from each other. Thus, the back pressure chamber receives the compressed refrigerant and the force from this compressed refrigerant forces the one scroll member toward the other, resisting the separating force.
In certain scroll compressors, it would be desirable to compress only a small volume of refrigerant. Thus, the separating force will be less than it would be in higher volume compression applications. Since the separating force is lower, it would be desirable to also have a lower back pressure force.
Typically, two seals define the back pressure chambers and have been concentric and circular. This raises a limitation on how small the back pressure chamber can be, and thus raises difficulties for designing back pressure chambers in smaller volume compressors. In particular, a minimum “orbit radius” is still required for the scroll compressor, even when the volumes are small. As the orbiting scroll orbits, the tap which taps refrigerant into the back pressure chamber, also orbits. Since there is a minimum amount of movement during this orbiting movement, the outer diameter of the seal which defines the back pressure chamber, must still be beyond the entirety of this orbit radius. Stated another way, the tap must be between the seals throughout the entire orbiting cycle.
One proposed scroll compressor has had its back pressure chamber offset relative to a center axis. The reason for this offset is to resist particular forces. In U.S. Pat. No 6,290,478, protecting this invention, a statement was made that the seal could be oval, oblong, or other non-circular shapes. The resultant back pressure chamber is offset relative to the center axis. This arrangement would not address the problem mentioned above, wherein it would still be desirable to have the back pressure chamber centered on a center axis, but simply have the back pressure chamber be smaller.